Yawing device and wind power plant comprising a yawing device

ABSTRACT

A damping coupling is provided to reduce the oscillations of the yawing device of a wind power plant. The damping coupling transmits forces from a driving device to a yaw drive, and the damping coupling is arranged and positioned in such a way that the transmitted moment is dependent on the difference in the rotational speeds between the input and the output shafts of the coupling. The damping coupling is preferably a hydrodynamic coupling.

TECHNICAL FIELD

The invention relates to a yawing device for a machinery according tothe preamble of claim 1. The present invention also relates to a windpower plant equipped with such a yawing device. Besides wind powerplants, the term machinery, such as defined in context with the presentinvention, also includes e.g. hoisting cranes, gun turrets etc. in whicha yawing device permits rotation of the machinery. Such a yawing deviceis known from the European patent application No. 0 110 807 A1.

BACKGROUND

The main objective of a yawing device in a wind power plant with ahorizontal wind turbine axis is to position the turbine into thedirection of the wind. The prior art yawing device comprises anelectrical or hydraulic motor and a high-ratio gear which acts on thetoothed path of the yaw bearing and thus turns the machinery into thedesired position. Due to the influence of e.g. wind shear the machineryis subjected to pulsating forces, both when yawing and when themachinery is stationary. These forces often have a dominating tendencyin one direction, which means that they tend to turn the wind turbineout of the direction of the wind. During yawing, coriolis forces arealso added.

These phenomena appear regardless of the number of turbine blades, butare less dominant on turbines with three or more blades. In many casesthe machinery has to include strong yaw brakes, which for some designsalso have to be partly activated when yawing, in order to avoid thedevelopment of damaging oscillations. Such oscillations initiallydevelop in yaw, but coupling with the rest of the machinery may resultin oscillations also in the blades and in the tower. Since wind powerplants have to be built very slender due to economical reasons, thesetendencies are strong. If the machinery is locked to the tower by meansof e.g. yaw brakes, the tower will be subjected to large yawing moments,while the tendency to oscillate remains.

Designs with or without yaw brakes may be supplemented with hydraulicdampers, composed of a hydraulic cylinder or a hydraulic pump/motor, theflow of which has to pass through a narrow orifice. The dampingcomponents may partly be identical with the hydraulic system thatexecutes the yawing of the wind turbine.

The European patent application No. 0 110 807 A1 discloses a wind powerplant where the impact of the damaging oscillations mentioned above areminimised. This is accomplished by installing a drive motor between theturbine of the wind power plant and the yaw bearing. This drive motor iscombined with a narrow orifice and thus acts as a damper. However, it iswell known in prior art that to achieve the damping effect with thisdrive motor, other components, such as valves, tanks, filters etc., haveto be added.

Even if the mentioned drive motor and its adjoining elements solves theproblem with the damping of the damaging oscillations, this solution hasa number of drawbacks. This drive motor and its adjoining elements areexpensive. It is shows complexity, i.e. installation and maintenancewill be expensive and time consuming. Finally the availability will beaffected, since the vulnerability of the device will increase with thenumber of elements added.

SUMMARY OF THE INVENTION

Thus, the object of the present invention is to provide a low-costyawing device in which not only the forces and the tendency tooscillations are substantially decreased but also the installation andmaintenance are simple to carry out.

This object is solved according to the features of the characterisingpart of claim 1.

Preferred embodiments of the invention are disclosed in the dependantclaims 2-9.

DESCRIPTION OF THE DRAWINGS

Different embodiments of the invention will now be described in detailwith reference to the accompanying drawings, in which

FIG. 1 shows a schematic view of a wind power plant disclosing a yawingdevice according to the present invention, and

FIG. 2 shows a preferred embodiment of the yawing device.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic view of a wind power plant comprising a windturbine 2, which drives and is carried by a gear-box 4, an electricalgenerator 6, a machinery bed 8, said machinery bed being the foundationfor the wind turbine 2, the gear 4 and the generator 6. Furthermore, themachinery bed 8 is connected to the yawing device 10 and to the yawbearing 12, which also is connected to a tower 14. In operation themachinery bed 8 and thus also the wind turbine 2, the gear-box 4 and thegenerator 6 are able to rotate around a yawing axis A.

FIG. 2 shows a preferred embodiment of the yawing device 10. The yawingdevice 10 comprises a yaw drive 16 interacting with the yaw bearing 12,optionally a yaw gear-box 18 which is connected to the yaw drive 16 inorder to increase the gear-ratio if needed, a connecting shaft 19,optionally an inertial mass 20 in order to further damp the damagingoscillations, and a damping coupling 22, which is provided between theinertial mass 20 and a driving device 24.

The damping coupling 22 transmits the yawing moment. With this coupling,the translated torque for each input rotational speed is a function ofthe difference in rotational speed between the input and output shafts.The relationship may be linear or may have other characteristics,depending on the design of coupling. The losses and thus the damping inthis type of coupling is determined by the difference in rotationalspeed and by the torque. In a preferred embodiment of the invention thisdamping coupling is constituted by a hydrodynamic coupling 22. Even ifthe invention will be described with a hydrodynamic coupling 22, it isobvious to a person skilled in the art that other types of similarcouplings can be used, e.g. couplings utilising magnetic fields andinduced electrical eddy currents in order to accomplish such a damping.

When yawing, the above mentioned hydrodynamic coupling 22 will affectboth the transmission of torque and the damping. When the wind powerplant is not yawing, the shaft of the hydrodynamic coupling 22 connectedto the driving device 24 is locked. In a preferred embodiment thelocking is performed by providing the driving device 24 with a holdingbrake 26. In this way the machinery will perform small, dampedoscillating yaw movements in the horizontal plane, which will decreasethe forces acting on the structure as compared to the case in which themachinery is totally locked in yaw. Thus the invention is a simple andefficient solution to the problem of damping the yaw movements bothduring yawing and when the machinery is not yawing.

In a preferred embodiment the invention also comprises an inertial mass20, which is connected with the high speed side of the yaw gear 18 andis provided prior to the mentioned hydrodynamic coupling 22, as shown inFIG. 2. Such an inertial mass 20 may be constituted by a separateflywheel or a similar device. It may also be an integral part of e.g.the hydrodynamic coupling 22.

Thus, the inertia of the inertial mass 20 will act on the machinery as awhole by a factor, which is proportional to the gear ratio squared.Since a typical ratio of a yawing device is 8000:1 (input speed for thedriving device 24, 1400 r/min, output yawing speed ca 1^(.)s), theinertial moment of the inertial mass will act round the yawing axis Aincreased by the factor 8000 squared, which is 64 million. This meansthat even a small inertial mass of a few kilograms in a substantial waywill influence the dynamics of a wind power plant, the machinery ofwhich has a weight of several tens of tons. By substantially is in thiscontext meant that the resulting moment of inertia of the machinery isincreased by around 10 percent or more. Generally this influence leadsto a decrease of the movements of the machinery, which contributes toprevent the development of dangerous oscillations. An excessive inertialmass is however not appropriate, since a minimisation of the movementsmay result in large internal forces in the yawing device.

In the preferred embodiment of the invention the yawing device includesboth a hydrodynamic coupling 22 and an inertial mass 20 that co-operatein an advantageous way. The damping is determined by the velocity andthe inertial forces are determined by the acceleration. Since velocityand acceleration having a sinusoidal movement exhibit a phase shift of90 degrees, also the damping and the inertial forces will exhibit aphase shift of 90 degrees. Thus the maximum momentary forces/movementsfor a certain amount of damping work will be less when the inertial mass20 and the hydrodynamic coupling 22 co-operate compared to when eitherof the two work independently. The decreased forces allow smallerdimensions of all the components that unite the wind turbine 2 with thetower 14.

The inertia of the machinery, the connecting shaft 19, the inertial mass20 and the hydrodynamic coupling 22 are all part of forming a dynamicsystem having a certain torsional natural frequency. The connectingshaft 19 is assumed to exhibit the spring characteristics of allelements that connect the machinery with the inertial mass 20 and thehydrodynamic coupling 22. In a preferred embodiment of the invention theproperties of these elements are adapted, arranged and positioned insuch a way that the natural frequency is well below the main excitationof the system, caused by the rotation of the wind turbine, since thiswill minimise the dynamic torques that are transferred through thesystem.

The driving device 24 of the yawing device is preferably an electricmotor that is connected to the hydrodynamic coupling 22 and the devicein such a way that it permits rotation at any selected rotational speed.Furthermore, the electric motor 24 may be provided with a holding brake26 that can lock one side of the hydraulic coupling 22 when the windpower plant is not yawing. In a preferred embodiment of the inventionthe electric motor is an alternating current (AC) motor 24 which isconnected to an electric frequency converter 28 that can be used forcontrolling the rotational speed of the AC motor under control by acomputer or a similar control device.

In a preferred embodiment the half of the hydrodynamic coupling 22,which is normally locked when not yawing, may be rotated at a suitablerotational speed by control of the converter 28 in order to compensatefor the inherent tendency of a wind turbine to drift out of the winddirection.

A yawing device according to the present invention is preferablyinstalled in wind power plants that lack yaw brakes, but may also beused in wind power plants that have such brakes.

A wind power plant may possess several yawing devices that work inparallel. By means of the present invention, the yawing moment can bedistributed evenly.

Although the present invention primarily has been described inconnection with wind power plants, it is obvious to a person skilled inthe art that the yawing device also may be used in connection withhoisting cranes, gun turrets or the like where damping and transmissionof yawing movements are needed.

It shall be understood that even if the description above shows specificpreferred embodiments to illustrate the present invention, a personskilled in the art will readily recognise from this teaching, and fromthe accompanying drawings and claims that various changes, modificationsand variations can be made therein without departing from the spirit andscope of the invention as defined in the following claims.

What is claimed is:
 1. A yawing device for a wind power plant, fortransmission and damping of yawing movements, comprising a yaw bearing(12) and a yaw drive (16) provided to permit rotation of the wind powerin yaw, a driving device (24) for driving the wind power in yaw and acoupling (22) for transmission of the moment from the driving device(24) to the yaw drive (16), characterised in that the coupling (22) issuch arranged and positioned that the moment transmitted by it isdetermined by the difference in rotational speeds of the input and theoutput shafts of the coupling (22).
 2. A yawing device as claimed inclaim 1, wherein the coupling is a hydrodynamic coupling (22).
 3. Ayawing device as claimed in claim 2, wherein an inertial mass (20) isprovided in such a way that the resulting inertial moment round theyawing axis (A) is increased.
 4. A yawing device as claimed in claim 3,wherein the inertia of the wind power plant, a connecting shaft (19),the inertial mass (20) and the hydrodynamic coupling (22) are adapted,arranged and positioned in such a way that the natural frequency of thesystem is below the excitation frequency.
 5. A yawing device as claimedin claim 2, wherein a brake (26) is provided for braking of the drivingdevice (24).
 6. A yawing device as claimed in claim 2, wherein thedriving device (24) is provided to admit rotation at selected rotationalspeeds.
 7. A yawing device as claimed in claim 2, wherein the drivingdevice is an AC motor (24) that may be controlled by a frequencyconverter (28).
 8. A yawing device as claimed in claim 1, wherein aninertial mass (20) is provided in such a way that the resulting inertialmoment round the yawing axis (A) is increased.
 9. A yawing device asclaimed in claim 8, wherein the inertia of the wind power plant, aconnecting shaft (19), the inertial mass (20) and the hydrodynamiccoupling (22) are adapted, arranged and positioned in such a way thatthe natural frequency of the system is below the excitation frequency.10. A yawing device as claimed in claim 9, wherein the inertial mass(20) is provided on the high speed side of a yaw gear (18) which isconnected to the yaw drive (16).
 11. A yawing device as claimed in claim9, wherein the inertial mass (20) is an integral part of the coupling(22).
 12. A yawing device as claimed in claim 8, wherein the inertialmass (20) is provided on the high speed side of a yaw gear (18) which isconnected to the yaw drive (16).
 13. A yawing device as claimed in claim8, wherein the inertial mass (20) is an integral part of the coupling(22).
 14. A yawing device as claimed in claim 8, wherein a brake (26) isprovided for braking of the driving device (24).
 15. A yawing device asclaimed in claim 8, wherein the driving device (24) is provided to admitrotation at selected rotational speeds.
 16. A yawing device as claimedin claim 8, wherein the driving device is an AC motor (24) that may becontrolled by a frequency converter (28).
 17. A yawing device as claimedin claim 1, wherein a brake (26) is provided for braking of the drivingdevice (24).
 18. A yawing device as claimed in claim 1, wherein thedriving device (24) is provided to admit rotation at selected rotationalspeeds.
 19. A yawing device as claimed in claim 18, wherein the drivingdevice is an AC motor (24) that may be controlled by a frequencyconverter (28).